Granular fertilizers have been used for some time to provide nitrogen to the soil. The most widely used and agriculturally important nitrogen fertilizer is urea. Most of the urea currently produced is used as a fertilizer in its granular (or prilled) form. However, after its application to soil, its hydrolysis to yield ammonia and carbon dioxide occurs. This process is catalyzed by the enzyme urease, which is produced by some bacteria and fungi. The gaseous products formed by the hydrolysis reaction (ammonia and carbon dioxide) volatilize to the atmosphere and thus, substantial losses from the total amount of the nitrogen applied to the field occur. The hydrolysis process can be considerably decelerated by urease inhibitors that are applied together with urea. Urease inhibitors can also be used in combination with nitrification inhibitors. Nitrification inhibitors are compounds which inhibit the conversion of ammonium to nitrate and reduce nitrogen losses in the soil. Examples of nitrification inhibitors include, dicyandiamide (DCD).
Examples of urease inhibitors are the thiophosphoric triamide compounds disclosed in the U.S. Pat. No. 4,530,714, including N-(n-butyl) thiophosphoric triamide (NBPT), the most developed representative of this class of chemicals. When incorporated into a urea-containing fertilizer, NBPT reduces the rate at which urea is hydrolyzed in the soil to ammonia. The benefits realized as a result of the delayed urea hydrolysis include the following: (1) nutrient nitrogen is available to the plant over a longer period of time; (2) excessive build-up of ammonia in the soil following the application of the urea-containing fertilizer is avoided; (3) the potential for nitrogen loss through ammonia volatilization is reduced; (4) the potential for damage by high levels of ammonia to seedlings and young plants is reduced; (5) plant uptake of nitrogen is increased; and (6) an increase in crop yields is attained. The use of NBPT is commercially available for the use in agriculture and marketed in such products as the AGROTAIN® nitrogen stabilizer product line.
Industrial grade N-(n-butyl) thiophosphoric triamide (NBPT) is a solid, waxy compound, and decomposes by the action of water, acid and/or elevated temperature. Accordingly, its combination with other solid materials is very difficult. The use of a liquid formulation of the NBPT is highly desirable because it greatly facilitates the introduction of the NBPT onto other solid materials, such as the PERGOPAK® M used in AGROTAIN DRY® and formulation with granular urea. The impregnation of NBPT onto a UFP, such as PERGOPAK® M or other solids, such as granular urea requires the NBPT to be introduced into some liquid carrier prior to being mixed with, the solid. The dissolution of NBPT with or without UFP into liquid urea-containing fertilizers, such as, urea-ammonium nitrate solutions (UAN), is also facilitated by having the NBPT in an easily assimilated liquid formulation.
However NBPT is very difficult to solubilize in a concentrated solution. Accordingly, a variety of solvent mixtures have been tried, including those disclosed in U.S. Pat. Nos. 5,352,265 and 5,364,438 (using N-methyl pyrrolidone, NMP); U.S. Pat. No. 5,698,003 (using propylene glycol or dipropylene glycol alone or in combination with NMP or poly(oxy-1,2-ethanediyl)-alpha (nonylphenyl)omega-hydroxy); and U.S. Pat. No. 8,048,189 (using ethanolamine, diethanolamine, triethanolamine, monoisopropanolamine, or diisopropanolamine buffered with acetic acid); PCT Patent Publication WO 2008/000196 (using dipropyleneglycol monomethylether, diethyleneglycol monomethylether, triethyleneglycol monomethylether or diethyleneglycol monobutylether in combination with polyvinylpyrrolidone (PVP) or NMP); CA Patent publication 2701995 (using water); U.S. Patent Publication Nos. 2010/0168256 (using water); 2010/0206031 and 2011/0259068 (using glycerol, aqueous sorbitol, ethanolamine, diethanolamine or triethanolamine); 2011/0113842 (using garlic essential oil in combination with sodium hydroxide or triethanolamine); and 2011/0233474 (using (S)-ethyl lactate or propylene carbonate in combination with tetrahydrofurfuryl alcohol, PVP, NMP, glycerol formal, propylene glycol and/or water).
However, both urea and solvents containing hydroxyl groups are hydroscopic which causes problems with NBPT formulations, especially with urea. Water can facilitate the decomposition of N-(n-butyl) thiophosphoric triamide (NBPT) into non-effective substances. In addition, water causes stickiness, clumping and caking of urea-based, granular fertilizers which reduces the flowability of urea-based granular fertilizers, and the like and complicates their handling. These problems are exacerbated during storage of these materials.
Accordingly, at least 10 wt. % of NMP or 0.1% of PVP is often used either as a co-solvent or as a crystallization inhibitor. However, amides like NMP and PVP can be health deleterious. N-methylpyrrolidone is often classified among teratogenic compounds and accordingly manufacturers must consider alternative solvents, especially where worker exposure is difficult to control (see e.g. Chemical & Engineering News: 32 (Jul. 21, 2008)). In addition, PVP has been documented to cause allergic reactions, particularly when applied to the skin or where it has come into contact with mucous membranes (see e.g. K. Yoshida et al. (2008) International Archives of Allergy and Immunology 146 (2): 169-73 (2008); A. Adachi et al. Contact Dermatitis 48 (3): 133-6 (2003); A. C. Rönnau et al. The British Journal of Dermatology 143 (5): 1055-8 (2000)).
The above mentioned disadvantages are overcome by the compositions of the present invention which provide compositions with reduced health risk and/or toxicity, lower volatility and flammability, increased stability of NBPT and other components in the composition, the ability to be used as lower application temperatures, and/or using commercially available, low cost materials.
The present invention relates to a composition comprising a urease inhibitor and an alkylene glycol alkyl ether solvent. The present invention also relates to methods of making the compositions and their use in agricultural applications.